Heat exchanger



FIG. 1 is a perspective view of a heat exchanger according to the invention.

FIG. 2 is a first side elevation view thereof.

FIG. 3 is a second side elevation view thereof.

FIG. 4 is a third side elevation view thereof; and,

FIG. 5 is a top plan view thereof.

The elements shown in broken lines are included for the purpose of illustrating environment and form no part of the claimed design. The portions shown in broken lines having unequal length segments illustrate the boundary of the claimed design and form no part of the claimed design. 

CLAIM We claim the ornamental design for a heat exchanger, as shown and described. 